Printed circuit boards containing wiring patterns and electronic components mounted thereon are vulnerable to damage or short circuiting as a result of mechanical contact with other circuit boards or objects. It therefore is desirable to encapsulate or insulate the boards, particularly in multiple circuit board environments. Accordingly, copending application Ser. No. 881,172 describes a technique to encapsulate a circuit board by wrapping the board with a shrink wrap tubing, then applying heat to shrink the tubing around the board and any components thereon.
While satisfactory, there still remains a need in some types of circuits that generate radio frequency (RF) energy to electrically shield the circuits and thereby prevent transmission of spurious RF energy therefrom that would tend to cause interference with neighboring equipment. Conversely, it is desirable to shield circuits sensitive to RF interference from RF generated from elsewhere.
An object of the invention, therefore, is to provide an RF shielded and electrically insulated circuit board structure.
Another object is to provide an RF shielded and electrically insulated circuit board structure using heat shrink tubing layers.
A further object of the invention is to provide a method of applying RF shielding and electrical insulation to a printed circuit board having electronic components mounted thereon.
Another object is to provide RF shielding and electrical insulation to a circuit board without adding significantly to the weight or cost of the board.
In accordance with these and other objects of the invention, an RF shielded and electrically insulated electronic circuit board structure comprises a circuit board and a first heat shrink tubing layer wrapping the circuit board and any wiring patterns and components thereon. An electrically conductive layer is located on the first heat shrink tubing layer and second heat shrink tubing layer is wrapped on the conductive layer to retain the conductive layer to the circuit board structure. The two layers of heat shrink tubing are in their shrunk condition to seal the circuit board and retain the electrically conductive shielding layer. Edge portions of the structure may be folded inward to prevent leakage of RF energy from the circuit board out through the edges.
In accordance with another aspect of the invention, the RF shielded and electrically insulated circuit board structure is made by wrapping a circuit board with a first layer of heat shrink tubing and applying heat to shrink the tubing to enclose the board and any wiring patterns and components thereon. An electrically conductive layer for RF shielding is applied on the first heat shrink tubing and the circuit board and electrically conductive layer are wrapped with a second layer of heat shrink tubing. Heat is applied to shrink the second tubing and thereby to retain the electrically conductive layer to the board. With any electrical wiring extending outward from the circuit board, edge portions of the tubing and RF shielding layers are folded inward to seal the edges of the circuit board structure.
Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiment of the invention are shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawing and description are to be regarded as illustrative in nature, and not as restrictive.